1. Field of the Invention
This invention relates to semiconductor devices of the type having a conductive lead frame with semiconductor chips and leads mounted on one side thereof, with a sealing resin applied to the one side.
2. Background Art
It is known to manufacture semiconductor devices by providing a lead frame assembly made up of a plurality of conductive unit lead frames interconnected by a tie bar network. Each unit lead frame has a support and associated leads. Semiconductor chips are mounted on the supports using heat resistant adhesive and electrically connected to the leads using conductive elements, such as wires. The supports are spaced from each other at predetermined intervals. A heat resistant sealing resin binder layer is applied to one side of the lead frame and, once cured to a hardened state, maintains the relative positions of the supports, semiconductor chips, and wires. Individual semiconductor devices are separated by cutting through the resin layer and lead frame at strategic locations.
In this conventional construction, the semiconductor chips and sealing resin are applied to only one side of the lead frame. The sealing resin is typically applied at a mold temperature of 180xc2x0 to 200xc2x0 C. However, due to the difference in the thermal expansion and contraction characteristics of the sealing resin and lead frame, warping of the resulting semiconductor device may result during the manufacturing process. This is particularly a problem with a thin semiconductor device. Cracks may form in the semiconductor device which may adversely affect conductivity. Additionally, the connecting leads may not be uniformly situated as a result of which the connection characteristics of the semiconductor devices may be compromised. Also, there is a tendency of the sealing resin to migrate to the bottom side of the semiconductor device forming mold xe2x80x9cflashxe2x80x9d over the leads that potentially blocks the conductive path to one or more leads. This flash may have to be removed. This potentially adds one or more steps to the manufacturing process and may increase the attendant costs.
In one form, the invention is directed to a method of manufacturing semiconductor devices. The method includes the steps of: providing a lead frame assembly having oppositely facing first and second sides; mounting a first semiconductor chip on the first side of the lead frame assembly; mounting a second semiconductor chip on the second side of the lead frame assembly; electrically connecting the first semiconductor chip to a first lead on the lead frame assembly; electrically connecting the second semiconductor chip to a second lead on the lead frame assembly; applying sealing resin to the first and second sides of the lead frame assembly with the first and second semiconductor chips mounted thereon; and after applying sealing resin, separating the lead frame assembly into first and second semiconductor devices. The first semiconductor device consists of a first portion of the lead frame assembly, the first semiconductor chip thereon, and the first lead electrically connected to the first semiconductor chip. The second semiconductor device consists of a second portion of the lead frame assembly, the second semiconductor chip thereon, and the second lead electrically connected to the second semiconductor chip.
The step of providing a lead frame assembly may involve joining first and second lead frame portions together, with the step of separating the lead frame assembly involving separating the first and second lead frame portions from each other.
In an alternative method, the step of providing a lead frame assembly may involve providing a conductive layer, with the step of separating the lead frame assembly involving cutting the conductive layer through a plane between the first and second sides of the lead frame assembly.
The method may further include the steps of mounting at least one additional semiconductor chip on each of the first and second sides of the lead frame assembly and electrically connecting each of the at least one additional semiconductor chips on the first and second sides of the lead frame assembly to a lead before applying sealing resin. The step of separating the lead frame assembly may involve the step of separating the lead frame assembly into first and second lead frame subassemblies. The first lead frame subassembly is defined by the first semiconductor chip and the one additional semiconductor mounted on the first side of the lead frame assembly. The step of separating the lead frame assembly may further involve cutting the first lead frame subassembly so as to define the first semiconductor device and a third semiconductor device consisting of a portion of the lead frame assembly with the one additional semiconductor chip mounted on the first side of the lead frame assembly so that the third semiconductor device is separate from the first semiconductor device.
The step of separating the lead frame assembly may involve separating the lead frame assembly into first and second lead frame subassemblies, with the second lead frame subassembly made up of the second semiconductor chip and the one additional semiconductor chip mounted on the second side of the lead frame assembly. The method may further include cutting the second lead frame subassembly so as to define the second semiconductor device and a fourth semiconductor device consisting of a portion of the lead frame assembly with the one additional semiconductor chip mounted on the second side of the lead frame assembly so that the fourth semiconductor device is separate from the second semiconductor device.
The step of applying sealing resin may involve using a mold to confine the sealing resin.
Through the mold, discrete masses of sealing resin may be applied over and around each of the first semiconductor chip and the at least one additional semiconductor chip on the first side of the lead frame assembly.
The step of cutting the first lead frame assembly may involve cutting between the discrete masses of sealing resin.
In one form, the step of joining the first and second lead frame portions involves using a sheet with first and second adhesive layers and adhering the first lead frame portion to the first adhesive layer and the second lead frame portion to the second adhesive layer.
The lead frame may have a sheet form.
In one form, the step of applying sealing resin involves applying a substantially uniform thickness of sealing resin continuously between the first semiconductor chip and the at least one additional semiconductor chip mounted on the first side of the lead frame assembly.
In one form, the first and second portions of the lead frame assembly each have a first thickness and the conductive layer has a thickness three to five times the first thickness.
The step of joining the first and second lead frame portions may involve joining the first and second lead frame portions using an adhesive. The step of separating the lead frame assembly may involve softening the adhesive to allow the first and second lead frame portions to be separated from each other.
In one form, the step of cutting the first lead frame assembly involves cutting using a cutting blade having a width on the order of 0.1 mm.
In one form, the adhesive has a higher melting point than the melting point for the sealing resin.
The adhesive may be at least one of a) a polyester-type hot melt binder, b) a polyimide-type hot melt binder, and c) a thermoplastic rubber-type binder.
The sealing resin may be an epoxy resin.
The first and second semiconductor devices may be the same.
In one form, the step of cutting the first lead frame subassembly involves cutting the first lead frame subassembly without cutting through the sealing resin on the first side of the first lead frame subassembly.
The step of cutting the first lead frame subassembly may involve cutting the first lead frame subassembly by cutting through the sealing resin on the first side of the lead frame subassembly.
The invention is also directed to a plurality of semiconductor devices made according to the process described above.